Host-based replication technologies exist for nearly every major operating system platform, including mainframe, Novell, Windows and most flavors of Unix. The free utilities that ship with the operating systems should only be used with offline applications or files. Look for a third-party solution if you need to maintain application availability while moving data to a new storage location. Products differ in the number of steps required to perform the data migration and how they manage the process.
There are a number of good reasons to use host-based technologies for data migrations such as:
Lack of money to purchase replication software
Inexperience with array- and network-based solutions
Comfort level with existing migration techniques
Integration with existing databases or a mix of different vendor's storage arrays
But before selecting a host-based tool, it's important to understand its pros and cons:
Pros:
Migrates from anything (internal or external disk) to anything
Inexpensive if used with existing OS utilities
Can change volume characteristics during migration
Cons:
Requires root-level access to each server
May need to install software in addition to migration software
Need to uninstall software following the migration
Administrators also need to consider if and how the utility handles periods of network latency. Not all data migrations will be from one array to another on a high-speed Fibre Channel (FC) network. As organizations consolidate data centers, data migrations will increasingly occur asynchronously over longer distances. So the utility must not only monitor the performance of the application on the server, but the speed of the migration. And the migration software must recover from interruptions that may occur during the data migration.
Tools such as Veritas' StorageCentral and Storage Reporter track data usage and profile storage resources--information essential for a successful data migration. Once the migration begins, Veritas' Storage Foundation analyzes the amount of disk space that will be saved and shows a progress bar as the data is migrated.
Look for products that monitor network traffic during data migrations, and in the event of a network slowdown, store all source changes and transmit them when possible. They should also perform resyncing operations to get the target data back in sync with the source data. And ensure the tools have a central management console from which to manage the migration.
About the author
Jerome Wendt is an independent writer specializing in the field of open systems storage and storage area networks. He has managed storage for small and large organizations in this capacity.
This article first appeared in Storage magazine.
